The present invention relates to a laminated structure comprising a copper metal substrate adhered to a polyimide resin film. More particularly the present invention relates to such a laminated structure having improved adhesion between the copper metal substrate and the polyimide film.
Laminates of copper foil and various polymers are well known in the art. Such laminates find industrial use in the preparation of electronic devices. Laminates of copper metal and polyolefin resins are employed as shielding tapes in armored cabled constructions. In U.S. Pat. No. 3,998,990 there are disclosed laminates of adhesive resins between various kinds of substrates. Particularly disclosed adhesive resins are in the form of metal containing copolymers consisting of monomeric units of ethylene, unsaturated carboxylic acids, unsaturated carboxylic acid metal salts, and unsaturated carboxylic acid esters. Such resins are excellent in workability and melt strength at the time of processing and also excellent in adhesiveness onto various kinds of substrates such as metals belonging to 1-B, II-B, III-A, IV-A, VI-B, VIII groups of the periodic table of the elements; glasses; polyolefins including homopolymers of .alpha.-olefins and copolymers containing .alpha.-olefins; polyamide resins; vinyl chloride resins; and vinylidene chloride resins.
Similarly, in U.S. Pat. No. 4,092,452 there is disclosed a plastic laminated metallic foil comprising a metal foil layer and a polyethylene, ethlene-vinyl acetate copolymer, ethylene unsaturated carboxylic acid ester copolymer or graft copolymer layer joined together by the use of an adhesive resin layer which could comprise inomeric derivatives of ethylene carboxylic acid copolymers.
In U.S. Pat. No. 4,132,857 there are disclosed electrical cables containing an improved adhesive layer for adhesion of the jacketing resin to the metal sheath. The adhesive resin comprised a dual layer film containing a film layer of an ethylene acrylic acid copolymer or an ethylene methacrylic acid copolymer or ionomer salts thereof and a film layer comprising polyethylene or an ethylene vinyl acetate copolymer.
The present invention relates to laminated structures comprising a copper metal substrate and a polyimide polymer layer. Such laminates are employed in the preparation of flexible electronic circuit boards. However, the obtention of satisfactory adhesion between a copper metal substrate and a polyimide film is exceedingly difficult. In order to obtain an acceptable level of adhesion (at least 4 pounds per lineal inch adhesion) the copper layer must be treated to provide a roughened surface. The procedure maximizes the surface area for adhesion and provides a mechanical interlock between the adhesive layer and the copper layer. For this purpose electrodeposited copper foil is generally used due to the roughened surface provided by the electrodeposition process. Where rolled copper foil is employed, strong oxidants must be applied to provide a roughened surface. This process is both expensive and a source of waste.
It would be desirable if there were provided a laminated structure comprising a copper metal substrate and a polyimide polymer layer said laminated structure having improved adhesion between the copper metal substrate and the polyimide polymer layer.
In addition it would be desirable if there were provided a laminated structure comprising a copper metal substrate and a polyimide polymer layer which may be prepared without the use of expensive conditioning processes to provide a roughened copper metal substrate surface.
Finally it would be desirable if there were provided a laminated structure comprising a copper metal substrate and a polyimide polymer layer which can be prepared in volume by contacting films of the various components utilizing short contact times at moderate temperature and pressure conditions.